Cyclone III device utilization issues

The fitter shouldn't run forever. From a compile-time perspective, the worst case scenario is a design that fits during placement but is really hard to route, in which case it spends a lot of time in the router and will then go back to re-trying placement with an emphasis on routing. It's a very special condition that seldom happens, and Cyclone III has lots of routing, so should almost never happen there. And if you're 50% full, it definitely won't happen. Are you getting messages? If not, what's the last one? What does "forever" mean?